This is an international, multicenter, uncontrolled open evaluation of chronic UT-15 plus conventional therapy in patients with pulmonary hypertension. UT-15 is an experimental medication that is administered chronically and subcutaneously. Subjects will have completed a 12-week doluble-blind, randomized trial (see SPID2734). This study is a treatment trial that will continue until the earliest of (1) three years from the date of entry of the first patient into this study, or (2) the commercial release of UT-15.